1. Field of the Invention
The present invention relates generally to a core slider of a magnetic head for a rigid magnetic disk drive, and a method for producing such a core slider, and more particularly to improvements of the core slider in its information reading and writing characteristics.
2. Discussion of the Prior Art
In the art of a rigid magnetic disk drive (RDD), there is known a floating-type magnetic head core slider which generally includes a slider body, and at least one yoke portion which cooperates with the slider body to form a closed magnetic path and define a magnetic gap open in a sliding surface. More specifically, the slider body has a pair of air bearing portions whose air bearing surfaces have a suitable height, and the sliding surface is provided on a track portion which is formed so as to extend across the magnetic gap, between the slider body and the yoke portion. The sliding surface of the track portion has a suitable width and the same height as the air bearing surfaces of the air bearing portions.
The core slider is roughly classified into three types, depending upon the position and number of the yoke portion or portions bonded to the slider body. The first type has one yoke portion (track portion) which is positioned in the middle of a distance between two air bearing portions. The second type has one yoke portion (track portion) which is formed so as to extend from one end of one of two air bearing portions. The third type has two yoke portions (track portions) each formed so as to extend from one end of the corresponding one of the two air bearing portions. In these three types of core slider, only one yoke portion (track portion) is used for writing (storing) and reading (reproducing) information on and from a magnetic disk, even where two yoke portions are provided.
The third type of core slider having two yoke portions, as well as the first and second types having only one yoke portion, is adapted such that one of the yoke portions is used to effect information writing and reading operations, and the other yoke portion is not associated with the information writing and reading operations. Namely, one of the two yoke portions cooperates with the slider body to form a track portion in which is open an information writing and reading magnetic gap.
In the known core slider, therefore, the writing and reading track portion formed between the yoke portion and the slider body should be constructed so as to provide acceptable characteristics in both reading and writing operations, even where the two yoke portions are provided. In other words, the core slider does not exhibit excellent "off-track" characteristics not only in the information reading from a magnetic disk, but also in the information writing on the magnetic disk.
In the RDD or rigid magnetic disk drive, an exclusive magnetic head is not provided, and new information is written over the previously stored or written information. Therefore, when new information is written over the previous information while the magnetic disk is in a floating or "off-track" condition with respect to the core slider, the previous information may be partially left unerased as undesirable remnant signals, which create noises upon reproduction of the newly stored information. This may lead to a lowered S/N ratio of the magnetic head, and an information reading error. To avoid the remnant signals, it is desirable that the writing width of the core slider be sufficiently larger than the reading width, so that the previous information may not be read, even if remnant signals may be left.
In the known core slider wherein a common track (track portion) is used for both writing and reading purposes, however, the writing width cannot be made sufficiently larger that the reading width, and the remnants cannot be effectively avoided. Thus, the S/N ratio, or the so-called "off-track" operating characteristics of the core slider cannot be sufficiently improved.
Where information writing and reading operations are effected by respective magnetic gaps, an optimum ratio of the size or length of the information writing magnetic gap in the longitudinal direction of the track to that of the information reading magnetic gap varies depending upon the coercivity of a recording medium, the thickness of the magnetic layer and the recording wavelength. Generally, the size of the writing magnetic gap should preferably be larger than that of the reading magnetic gap. However, where the same maganetic gap is used for both reading and writing operations, the size of the gap is determined so as to provide a compromise or balance between the reading and writing characteristics. In this case, it is difficult to make the best use of the properties or characteristics of the recording medium, and therefore difficult to obtain a sufficiently high density of information storage per unit area of the recording medium. This means a relatively low storage capacity of the medium.